New Zealand has traditionally relied on clover and other legumes to biologically fix the nitrogen that is required to grow pasture. More recently, there has been increased use of nitrogen fertilisers such as urea to increase pasture production further and address seasonal deficits in feed supply.
There are a number of negative environmental consequences of excessive use of nitrogen fertilisers. The one that is most publicised is the potential to increase the level of nitrates that are leached into groundwater and can therefore pollute waterways. There are also implications relevant to the concern over greenhouse gases. The use of high amounts of nitrogen fertiliser can increase the level of denitrification that can occur leading to higher levels of nitrous oxide emissions (a potent greenhouse gas). Furthermore, the production of artificial nitrogen fertiliser is highly energy intensive; this energy requirement is derived from the burning of natural gas resulting in the production of the other greenhouse gas, carbon dioxide. This also represents a significant use of a limited natural gas resource increasingly important for other uses including electricity generation.
Use of nitrogen fertiliser is steadily increasing. In New Zealand, a country with an economy that relies heavily on dairy, sheep and beef farming, total fertiliser use increased by 113 percent from 1986 to 2002 (Statistics New Zealand, Fertiliser use and the environment, August 2006). The application of urea increased by approximately 27 percent between 2002 and 2004 (ibid.).
A problem with the application of nitrogen fertilisers is that often excess nitrogen is applied to the pasture. In addition, if nitrogen is not applied at the correct time, for example, if it is applied when plants are not actively growing, the loss of nitrogen is exacerbated. There are several approaches that have been taken to minimise adverse effects of fertiliser use. One such approach is the use of nitrification inhibitors.
The most common nitrification inhibitors are 2-chloro-6(trichloromethyl)pyridine, dicyandiamide and 3,4-dimethylpyrazole-phosphate. Such inhibitors act to reduce nitrate leaching and nitrogen oxide emissions. Plant growth is increased. However, the effects can be variable and depend on timing of application, amount of nitrogen fertiliser applied and physical factors such as soil temperature, moisture, and pH.
Urease inhibitors have also been used to prevent loss of nitrogen to the atmosphere by volatilisation as ammonia. Urease inhibitors act by slowing the rate of hydrolysis. Other ways of reducing nitrogen loss are through farm management practices, including timing of application of fertiliser, split fertiliser applications, grazing management, pasture species choices, cropping type and landscape modification.
However, there remains a need for new products and methods for improving plant growth responses and development, while reducing nitrogen input.